1. Field
One embodiment of the invention relates to a communication method and communication system for making voice communication between telephone terminals via an Internet Protocol (hereinafter “IP”) network such as an IP telephone system.
2. Description of the Related Art
In recent years, IP telephone networks, namely a network telephone system adapted for real-time transmission and reception while handling an image or a voice as packet data in a bi-directional manner via a packet network, has been prevailingly popular. For IP telephone systems, a plurality of IP telephone terminals are connected in a private network such as a Local Area Network (hereinafter “LAN”), and the private network is connected to a public network or a global network such as the Internet via a router device. The router device performs address conversion, thereby enabling multimedia information communication between the multiple IP telephone terminals over the global network. In this case, the plurality of IP telephone terminals connected to the private network and the global network are handled as extension terminals of an exchange apparatus.
In the meantime, the above-described system incorporates a Network Address Translator (herein after “NAT”) function in the router device. The NAT function is provided as a function for employing one IP address which has been allocated in advance for connection, thereby converting a private address into a global address to transmit the converted address as a transmission source IP address, followed by converting a global address of an IP address which is an address to be supplied in reception into a private address. Such an NAT function is described in an Request For Comments (RFC) 1631, and it is disclosed by, for example, Japanese Patent Application Publication (KOKAI) No. 2003-289318, Japanese Patent Application Publication (KOKAI) No. 2002-368773, and Japanese Patent Application Publication (KOKAI) No. 2003-324482.
In the above-described system, during transmission of a voice packet, an IP address and a port number are included with a header area of an User Datagram Protocol (hereinafter “UDP”) packet are converted by a router device. However, an IP address and a port number included a data area of the UDP packet are not converted. Therefore, making it possible to connect an IP telephone terminal as extension of a main device, but making it substantially unable to communicate a voice data.
In order to solve this problem, development of a Virtual Private Network (hereinafter “VPN”), an Application Level Gateway (hereinafter “ALG”), a Simple Traversal of UDP Through NAT (hereinafter “STUN”) protocol and the like is proposed.
However, in all of these schemes, any software which may convert an IP address and a port number included in a data area of the UDP packet, needs to be packaged for an IP telephone terminal or a router device, and therefore, the existing terminals and routers cannot be uniformly utilized as they are, forcing a user to expose a burden on cost efficiency or scheduling.